MARK DUNN, Senior National Reporter

OTTAWA - Liberal MP Marc Garneau, a Canadian hero and the country's first astronaut in outer space, will set his sights on a new frontier when he announces next week he wants to become prime minister.

The Montreal politician, 63, will make his Liberal leadership ambitions official at the mid-week caucus meeting on Parliament Hill and then hold a media event afterwards, a source confirmed.

But Garneau's parliamentary assistant disputed his boss' intentions, saying the Liberal House leader is still mulling whether to run and that no announcement is planned for Nov. 21.

"Mr. Garneau has not made a decision on whether to enter the leadership and subsequently no date has been set for an announcement," Jean Proulx said.

But Garneau's entry into the race to replace Michael Ignatieff, who stepped down a day after the party's crushing loss in last year's election, has been widely expected.

The Liberal House leader is considered a serious contender in a contest that officially began Wednesday and ends in April when the new leader is crowned.

A temperamental Justin Trudeau stumbled out of the blocks Wednesday when he lashed out at a Sun News Network reporter during a campaign stop in a riding the Liberals are expected to lose in a byelection later this month.

Garneau brings among the strongest resumes to a race party officials are counting on to re-energize the party.

The former head of the Canadian Space Agency became an overnight hero in 1984 when the space shuttle Challenger lifted off with him aboard - the first of three shuttle missions for the Quebec native.

The leadership race could have as many as 10 individuals vying for the top job by the end of next week if Liberal MP Joyce Murray tosses her hat into the ring.